Method of fabricating a light-emitting device having a planarized color filter

ABSTRACT

A light-emitting device and the fabrication method thereof. A substrate is provided. A plurality of active elements are formed on the substrate, defining a plurality of pixel areas. A color filter is formed on the pixel areas. The surface of the color filter is planarized to reduce roughness. An electrode is formed on the color filter. An light-emitting layer is formed on the electrode. A second electrode is formed on the light-emitting layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device, and moreparticularly to a light-emitting device with a color-filter-on-arraystructure.

2. Description of the Related Art

With recent interests and development, organic light-emitting diode(OLED) devices have become a potential candidate to replace LiquidCrystal Displays (LCDs) for next-generation display. With their activelight-emitting characteristics, OLED devices, unlike LCDs, do notrequire a backlight module to provide a light source, benefiting theirweight reduction. In addition, OLED devices provide high resolution andquick response, and a wider viewing angle (to 160°) than LCDs.

OLED devices utilize an organic light-emitting diode to provide thelight source. The organic light-emitting diode uses an organic layer asan active layer, sandwiched between an anode and cathode electrodes toform a stacked layer. At least one of the electrodes is transparent toallow light transmission.

FIG. 1 is a cross-section view of a conventional OLED device. The OLEDdevice 1 includes a substrate 2, monochromatic light-emitting diodes 3,and thin film transistors 20. Monochromatic light emitted from a activelayer 30 of the light-emitting diodes 3 converts to red, green or bluelight respectively after passing through a red 81, green 82, or blue 83color-filtering unit. The substrate 2 is a transparent substrate of, forexample, glass or polymer. As a polymeric substrate, the substrate 200can be made of polyethyleneterephthalates, polyesters, polycarbonates,polyacrylates or polystyrenes. Furthermore, the color-filtering unit isformed by, for example, pigment dispersion, dyeing, electrodeposition,or printing

In FIG. 1, an indium-tin-oxide (ITO) layer is formed over the substrate2 to serve as a transparent anode 31, with a counter cathode electrode32 of a low-work-function metal or alloy, such as Ca, Al, MgAg or AlLi.

In the conventional OLED device, the color-filtering units 81, 82 and 83generally have severe surface roughness Ra around 20 nm. If thetransparent anode electrode 31 is directly formed on the color-filteringunits 81, 82 and 83, the surface roughness of the transparent anodeelectrode 31 is definitely affected, thereby resulting in a surfaceroughness also around 20 nm. In addition to failure to fulfill therequirements of an OLED device (preferred surface roughness of theelectrode less than 10 nm), short circuit and current-leakage may alsobe caused, deteriorating performance.

To avoid the above shortcomings, a additional planarization layer 5 mustbe placed between the transparent electrode 31 and the color-filteringunits 81, 82 and 83, to avoid the inherent surface roughness ofcolor-filtering units 81, 82 and 83 affecting subsequent electrodeformation. However, the process complexity is increased, resulting inhigh manufacturing costs and time-consuming.

Therefore, it is necessary to develop a simple and efficientmanufacturing method for an OLED with a color-filter-on-array structureto obtain OLEDs having smoother transparent electrode surfaces.

SUMMARY OF THE INVENTION

Accordingly, the present invention is to reduce the surface roughness ofthe color filter by direct planarization of the color filter withoutproviding a separate planarization layer on the color filter to supportplanar-electrode formation. This simplifies light emitting devicefabrication and improves performance.

In one aspect of the present invention, the color filter is planarized,after being formed on the active matrix substrate to complete a COAstructure, to reduce surface roughness and ensure a planar surface ofthe consequential electrode.

In one embodiment, the method of fabricating a light-emitting device,comprises the steps of providing a substrate, forming a plurality ofactive elements on the substrate, forming a color filter on thesubstrate, planarizing the surface of the color filter to reduceroughness, and forming a first electrode on the color filter. Theinvention may further comprise the steps of forming an light-emittinglayer on the first electrode, forming a second electrode on thelight-emitting layer, and disposing a second substrate on the secondelectrode, facing the substrate.

The invention further provides a light-emitting device, comprising acolor filter on an active matrix substrate, with a surface roughness(Ra) of less than 10 nm, a first electrode on the color filter, with asurface roughness (Ra) of less than 10 nm, a light-emitting layer on theelectrode, a second electrode on the light-emitting layer, and asubstrate on the second electrode, facing the active matrix substrate.

In one embodiment, the surface roughness (Ra) of the color filter isplanarized to less than 10 nm, and the first electrode is formed havinga surface roughness (Ra) less than 10 nm.

The surface of the color filter can be planarized by, for example, UVtreatment, O₂ plasma treatment or polishing, wherein UV treatment canbe, for example, an excimer UV treatment or a corona treatment. Thepolishing can be, for example, chemical mechanical polishing. Both thecolor filter and the first electrode are preferably polished. The colorfilter can be, for example, planarized by plasma that exposure to Ar, O₂or H₂O before formation of the ITO electrode to reduce surface roughness(Ra) to less than 10 nm.

The first electrode can be, for example, indium tin oxide (ITO), and thesecond electrode can be, for example, Ca, Al, Mg, MgAg, AlLi orcombinations thereof. In one embodiment, the method includes planarizingthe surface of the first electrode.

The first electrode, light-emitting layer and second electrode may forma monochromatic light-emitting device. The monochromatic light-emittingdevice can be, for example, a white-light light-emitting device.

The light-emitting layer can be, for example, a stacked layer of anelectron-injecting layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injecting layer. The activeelements may comprise an amorphous-Si thin-film transistor or a poly-Sithin-film transistor.

In one embodiment, the present invention is also directed to an organiclight-emitting device, which may comprise a color filter on an activematrix substrate, with a surface roughness (Ra) of less than 10 nm, anelectrode on the color filter, with a surface roughness (Ra) of lessthan 10 nm, an organic light-emitting layer on the electrode, a secondelectrode on the organic light-emitting layer, and a substrate on thesecond electrode, facing the active matrix substrate.

DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a cross-section view of a conventional OLED device;

FIG. 2 is a schematic top view illustrating an organic light emittingdevice according to the present invention;

FIG. 3 is a sectional diagrams along line A-A′ of FIG. 2;

FIGS. 4A to 4E are sectional diagrams along line A-A′ of FIG. 2illustrating the manufacturing process of the organic light emittingdevice according to the present invention;

FIG. 5A is a close-up cross-section view of location 5A shown in FIG.4B;

FIG. 5B is a close-up cross-section view of location 5B shown in FIG. 4Cafter planarization;

FIG. 6 is a schematic drawing of an electronic device incorporating theorganic light emitting device shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in connection with the embodiments oforganic light-emitting devices. However, it is within the scope andspirit of the present invention to apply to other types oflight-emitting devices, such as polymer light-emitting devices,chemiluminescent devices, backlit LCD, etc.

FIG. 2 is a schematic top view of an organic light-emitting deviceaccording to the present invention. The organic light-emitting device100 comprises a plurality of pixel areas arranged in a matrix form. Eachpixel area comprises a TFT 101 electrically connected to a data line102, a capacitor 103, an organic light-emitting diode 105, and anotherTFT 220 electrically connecting to the organic light-emitting diode 105.FIG. 3 is a sectional diagrams along line A-A′ of FIG. 2, and FIGS. 4Ato 4E are sectional diagrams along line A-A′ of FIG. 2 illustrating themanufacturing process of the organic light-emitting device according toa embodiment of the present invention.

FIGS. 4A-4B illustrate the fabrication of an active matrix substrate 300with a color-filter unit 208. The active matrix substrate 300 of theinvention may be a transparent substrate 200 of, for example, glasssubstrate, with an a-Si-TFTs array or an LTPS (low temperature polysilicon) TFTs array.

In the embodiment, an active matrix substrate of an LTPS array, withtop-gate TFTs, is used to explain the inventive organic light-emittingdevice and the fabrication method thereof. However, an active matrixsubstrate with bottom-gate TFTs is applicable as well.

In FIG. 4A, a substrate 200 is provided with a buffer layer 202 formedthereon. A plurality of top-gate LTPS-TFTs 220 are formed on the bufferlayer 202, wherein the top-gate LTPS-TFT 220 includes a gate electrode250, a source electrode 251, a drain electrode 221, a gate insulatinglayer 204, a channel region 255, and a source/drain region 256. Thedrain electrode 221 couples to the source/drain region 256 via a contacthole 257 of a dielectric layer 206. The dielectric layer 206 has apredetermined area 207 defined for color-filter formation, on which anorganic light-emitting unit will be formed thereon subsequently.

The LTPS-TFTs 220 serve as controlling units of the organiclight-emitting device.

In FIG. 4B, a color filter 208 is formed on the predetermined area 207.The color filter 208 may be a red, green, or blue color-filtering unit,or a combination thereof to achieve a full-color display.

FIG. 5A is a close-up cross-section view of location 5A shown in FIG.4B. Owing to the severe surface roughness of the color filter 208, thedirect deposition of a following electrode may result in a rough finalsurface. Therefore, a feature step of the invention is performed herein,to planarize the surface of the color filter 208.

The color filter 208 can be planarized by, for example, UV treatment, O₂plasma treatment or polishing. The UV treatment can be, for example, anexcimer UV treatment or a corona treatment. The excimer UV treatment canbe performed, for example, with a UV light of 200-400 nm for 10-120seconds. The corona treatment can be performed, for example, by aconventional or 3-D corona treatment system. The polishing treatment canbe, for example, chemical mechanical polishing. In addition to polishingthe color filter 208, the electrode formed thereon may be polished toensure a planar surface.

In addition, the O2 plasma treatment can be exposure to Ar, O2 or H2Oduring the formation of the electrode to reduce surface roughness (Ra)of the color filter to less than 10 nm.

In the embodiment, an excimer UV light with a wavelength of 308 nm isapplied to planarize the color filter 208. FIG. 5B is a close-upcross-section view of location 5B shown in FIG. 4C after planarization.The surface roughness Ra of the color filter 208′ after planarizationfor various periods is listed in Table 1. According to Table 1, thesurface roughness Ra of the color filter 208′ is effectively reduced toless than 10 nm, ensuring that final surface roughness of the electrodeis less than 10 nm as well, fulfilling the requirements of an OLEDdevice.

TABLE 1 Results of Excimer UV Treatment Treating time surface roughnessRa No. (sec) (nm) 1 10 7.4 2 25 8.0 3 60 7.1 4 120 6.4

FIGS. 4C-4E are cross-section views to illustrate the subsequentfabrication of the OLED device. In FIG. 4C, a transparent electrode 212is formed on the planarized color filter 208′. A transparent conductivelayer 212 is first conformally formed on the drain electrode 221 of theLTPS-TFT 220, and then the electrode 212 is defined by lithography andetching (e.g., by dry or wet etching) to remove a part of thetransparent conductive layer 212. The transparent conductive layer 212may be a layer of indium tin oxide (ITO), indium zinc oxide (IZO),aluminum zinc oxide (AZO) or zinc oxide (ZnO), formed by sputtering,electron-beam evaporation deposition, thermal evaporation deposition,chemical vapor deposition or spray pyrolysis. The surface of thetransparent conductive layer 212 may be further planarized by, forexample, chemical mechanical polishing. This planar surface of thetransparent conductive layer 212 helps to ameliorate short circuit andcurrent leakage.

In FIG. 4D, an insulating layer 214 is formed on the transparentconductive electrode 212. The insulating layer 214 is then etched, usingthe transparent electrode 212 as an etchstop, to define a predeterminedarea 222 for an organic light-emitting layer on the transparentconductive electrode 212.

In FIG. 4E, an organic light-emitting layer 230 is formed on thepredetermined area 222 and the insulating layer 214, allowing contactbetween the organic light-emitting layer 230 and the transparentconductive electrode 212. The organic light-emitting layer 230 may be ofsmall-molecule or polymeric organic light-emitting materials.

In the embodiment, the organic light-emitting layer 230 can be made fromwhite-light-emitting materials including an electron-injecting layer701, an electron transport layer 702, an emitting layer 703, a holetransport layer 704 and a hole-injecting layer 705.

Finally, referring to FIG. 3, an electrode 240 is formed on the organiclight-emitting layer 230, with contact therebetween to serve as acathode of a OLED 150, and a substrate 200′ is disposed on the cathodeelectrode 240, facing the substrate 200. The electrode 240 may be formedby vacuum thermal evaporation deposition or sputtering. To serve as thecathode of an organic light-emitting diode 105, materials with alow-work function are preferable, such as Ca, Al, Mg, MgAg, AlLi, inwhich Mg, Mg—Ag alloy, or a stack of Mg/MgAg and ITO are morepreferable.

The organic light-emitting device of the embodiment comprises, as shownin FIG. 3, the planarized color filter 208′ on the active matrixsubstrate 200, the anode electrode 212 on the planarized color filter208′, the organic light-emitting layer 230 on the anode electrode 212,the cathode electrode 240 on the organic light-emitting layer 230, andthe substrate 200′ on the cathode electrode 240, facing the activematrix substrate 200, wherein the surface roughness of the planarizedcolor filter 208′ and the anode electrode 212 are less than 10 nm. Theorganic light-emitting layer 230 comprises the electron-injecting layer701, electron transport layer 702, emitting layer 703, hole transportlayer 704 and the hole-injecting layer 705.

Accordingly, by planarizing the color filter 208, surface roughness isreduced, and a planar surface of the anode electrode 212 is ensured.

Furthermore, without requiring a planarization layer between the colorfilter 208 and the anode electrode 212, the surface roughness of thecolor filter 208 and the anode electrode 212 are reduced, simplifyingfabrication and improving performance.

FIG. 6 is a schematic drawing of an electronic device incorporating theorganic light emitting device shown in FIG. 2. The electronic device 400includes a controller 300 operatively coupled to the organic lightemitting device 100 for controlling operation of organic light emittingdevice 100. The electronic device can be, for example, a mobiletelephone, a personal computer, or a personal digital assistant (PDA).

The foregoing description has been presented for purposes ofillustration and description. Obvious modifications or variations arepossible in light of the above teaching. The embodiments were chosen anddescribed to provide the preferred illustration of the principles ofthis invention and its practical application to thereby enable thoseskilled in the art to utilize the invention in various embodiments andwith various modifications as are suited to the particular usecontemplated. All such modifications and variations are within the scopeof the present invention as determined by the appended claims wheninterpreted in accordance with the breadth to which they are fairly,legally, and equitably entitled.

1. A method of fabricating a light-emitting device, comprising the stepsof: providing a substrate; forming a color filter on the substrate;planarizing a surface of the color filter; and forming a first electrodecontacting the color filter.
 2. The method as claimed in claim 1,wherein the step of planarizing a surface of the color filter includesplanarizing the surface of the color filter to a surface roughness (Ra)less than 10 nm.
 3. The method as claimed in claim 1, wherein the stepof planarizing a surface of the color filter comprises performing on thesurface of the color filter a UV treatment, an O2 plasma treatment, or apolishing.
 4. The method as claimed in claim 3, wherein the step ofperforming a UV treatment comprises performing an excimer UV treatmentor a corona treatment.
 5. The method as claimed in claim 1, furthercomprising the step of planarizing a surface of the first electrode. 6.The method of claim 5, wherein the step of planarizing a surface of thefirst electrode includes performing on the surface of the firstelectrode a UV treatment, an O2 plasma treatment, or a polishing.
 7. Themethod as claimed in claim 3, wherein the step of performing a polishingincludes chemical mechanical polishing.
 8. The method as claimed inclaim 1, further comprising the steps of forming an organiclight-emitting layer on the first electrode and forming a secondelectrode on the organic light-emitting layer.
 9. The method as claimedin claim 8, wherein the first electrode, the organic light-emittinglayer and the second electrode comprise a monochromatic organiclight-emitting diode.
 10. The method as claimed in claim 8, wherein theorganic light-emitting layer is a stacked layer comprising anelectron-injecting layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injecting layer.
 11. Themethod as claimed in claim 1, wherein the substrate comprises atransparent substrate.
 12. The method as claimed in claim 1, wherein thefirst electrode comprises a transparent conductive material includingindium tin oxide (ITO) or indium zinc oxide (IZO).
 13. The method asclaimed in claim 3, wherein the step of performing an O2 plasmatreatment includes exposing the color filter to Ar, O2 or H2O before thestep of forming the first electrode.
 14. The method as claimed in claim8, wherein the second electrode comprises a conductive materialincluding one of Ca, Al, Mg, MgAg, AlLi or a combination thereof. 15.The method as claimed in claim 8, further comprising forming activeelements on the substrate, wherein the active elements comprise anamorphous-Si thin-film transistor or a poly-Si thin-film transistor.